The present invention relates to a transport system for conveying a workpiece from a first medium or chamber into a second medium or chamber, essentially without one affecting the other. Further it relates to a method for charging and unloading a treatment chamber with a selected treatment atmosphere differing from the chamber medium.
Further the present invention relates also to a vacuum chamber with a transport system as mentioned, as well as use of the transport system or of the vacuum chamber.
A transport system is known from European Patent Application EP-A-0 242 997 for transferring workpieces from a workpiece magazine of a first medium into a treatment chamber, such as a vacuum chamber, of a second medium, thence into a third medium, etc. The transport system from one chamber into the other comprises a two-armed lever which is disposed between the chambers and can be flapped into both. This lever is integrated in a sealed valve arrangement by means of which the chambers can be separated from or connected with each other under seal. This sealing valve arrangement is designed similar to a gate, so that the two respective chambers and hence their atmospheres are either connected or separated from each other.
Such a transport system has the disadvantage that with each lever rotation into one of the two respective chambers the two chambers are connected, whereby an equalization of the respective atmospheres occurs. If it is necessary to work in one of the chambers with an operating atmosphere that is kept within narrow tolerances, this procedure requires that after each transport process involving the two chambers, the chamber must be conditioned anew.
Hence the transport system shown there is unable to convey a workpiece from a first to a second medium substantially without one affecting the other.
Further it is known from European Patent Application EP-A-0 246 798 to provide transport levers inside each of a set of serially connected treatment chambers, a lever in a particular chamber operating in said chamber as well as reaching over into the next chamber. Here, too, two treatment chambers in question communicate during a transport process involving them, so that thereafter, because of their atmosphere having been influenced by adjacent chambers, the respective chambers must be conditioned anew if the treatment atmospheres of each of the chambers in question must be maintained within narrow tolerances and the atmospheres in the chambers in question are different.
Likewise, it is known from U.S. Pat. No. 4,553,069 to provide, in a vacuum chamber, a pantograph-like, multi-armed transport lever mechanism. To remove workpieces to be treated, such as wafers, from a magazine, one reaches from the vacuum chamber through a then open slot valve into the magazine, whereby again a connection is established between magazine and vacuum chamber, and this makes it necessary, in the case where delicate vacuum conditions must be maintained within narrow tolerances, to condition the vacuum chamber anew after a transport process.
In addition, providing the transport arm with associated parts in the vacuum chamber, as in EP-A-0 246 798 also, results in a relatively large chamber volume with a respective cost due to pumping capacity and conditioning times, since the volume in the vacuum chamber that is made available for the transport system, must be conditioned as well.
Also from U.S. Pat. No. 4,670,126 it is known to provide, in an intermediate chamber between several treatment chambers, a multi-armed transport lever which can selectively reach into one of the existing connected treatment chambers, via gates with slit-valve type closures. The multi-armed transport lever which is able to extend into the connected chambers results in a relatively large volume for the intermediate chamber, which, during each transport to one of the connected treatment chambers, communicates with that chamber, so that interaction of atmospheres takes place and hence after each such transport process the respective treatment chamber must be conditioned anew, and possible also the intermediate chamber.
From U.S. Pat. No. 4,733,746 it is further known to charge a vacuum treatment chamber bilaterally via two vacuum antechambers, by means of a transport system which is not shown in detail in that reference.
Further a specific transfer cycle is described, from an antechamber into the vacuum chamber and into the next antechamber, all three chambers being connected together, whereby relatively large volumes, namely those of the intermediate chambers, affect the vacuum chamber.
U.K. Patent Application GB-2 143 494 discloses a transport system consisting of a lock chamber in which a two armed pivoting lever is mounted substantially centrally in the chamber and can be moved out through conventional slit valves. As the two arms of the transport lever are driven separately, the receiving end portion of the lever can be controlled in practically any curvilinear path. On the other hand, this transport system is disadvantageous in the sense that the drive and the respective lead-throughs for the two lever arms are extremely complicated with respect to vacuum tightness and that the chamber is relatively big, adversely affecting pump units to be installed or their capacity and operating times.
Further, reference is made to European Patent Application EP-OS 0 291 690.